Spatiotemporal analysis of long-term air pollution in two urban regions of Vietnam and potential source contributions

Abstract

Air quality monitoring in Vietnam has been limited by sparse ground-based observations, leaving long-term pollution dynamics poorly understood. This study provides the first 43-year (1980–2023) spatiotemporal assessment of major pollutants including carbon monoxide (CO), sulfur dioxide (SO₂), black carbon (BC), and fine particulate matter (PM_2.5), across Vietnam's two largest urban–industrial regions. In addition, we combined remote sensing data, ground-based PM_2.5 data, statistical analyses, and source attribution modeling to disentangle local and transboundary influences on air quality in Vietnam. Overall, the concentrations of air pollutants were consistently 2–4 times higher in the North than in the South during the last five years (CO: 2.30; SO₂: 4.43; BC: 3.40, PM₂₅: 4.14 times). BC was strongly correlated to PM_2.5 (ρ up to 0.97, p < 0.01), demonstrating its central role in PM_2.5 composition. The Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2) reproduced seasonal PM_2.5 variability in Hanoi (ρ = 0.64 ÷ 0.82) but underestimated dry–wet contrasts in Ho Chi Minh City, emphasizing the need for enhanced ground-based monitoring. Results of potential source contribution function (PSCF) highlighted northern PM_2.5 hotspots associated with transport from neighboring countries, while southern hotspots were more diffuse and strongly influenced by traffic, industrial, and shipping emissions. Moderate Resolution Imaging Spectroradiometer (MODIS) fire data confirmed biomass burning in the Mekong subregion during March–April as a significant episodic contributor to northern PM_2.5. The findings of this study provide a robust baseline for emission trend evaluation, targeted mitigation, and cross-border pollution management, offering critical evidence to support Vietnam's net-zero emission strategies.